1. Field of the Invention
The present invention relates to a bent work to be used as a bearing-receiving unit and the like for construction machinery, a bending method for manufacturing the same, and a bending device to be used therefor.
2. Description of the Related Art
Generally, construction machinery such as a hydraulic shovel includes, as shown in FIG. 19, a lower moving unit 51 and an upper rotational unit 52 rotatably supported by the lower moving unit 51. The upper rotational unit 52 is rotatably mounted on the lower moving unit 51 via a bearing-receiving unit 53 fixed to the lower moving unit 51 and a bearing (not shown) fixing to the bearing-receiving unit 53. As shown in FIGS. 20 to 22, the bearing-receiving unit 53 includes a cylindrical part 54, and a flange 55 protruding toward the outside or outwardly at the upper end of the cylindrical part 54. The flange 55 is provided with a number of through-holes 55a (four through-holes 55a are shown in FIGS. 20 and 21) formed in the flange 55 for receiving bolts (not shown) for fixing the bearing. The bearing-receiving unit 53 must have a strength sufficient to support the bearing thereon. The cylindrical part 54 and the flange 55 are made of a thick steel plate (the cylindrical part 54 is thinner than the flange 55).
Hitherto, the bearing-receiving unit 53 has been manufactured in a manner such that a first member 57 made of a thick steel plate bent in a cylindrical shape and a second member 58 made of a thick steel plate bent in an annular shape are welded to each other (see FIGS. 23 and 24). In FIG. 24, welds 59 are shown. In FIG. 23, the first and second members 57 and 58 are welded to each other butt-welds 57a and 58a, respectively. A roll-forming method for manufacturing the first and second members 57 and 58, as shown in FIGS. 25 to 29, is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 7-314050.
In the roll-forming method, four rolls, which are a pair of upper and lower press-rollers 61 and 62, an inlet assist roller 63 disposed at the inlet side, and an outlet assist roller 64 disposed at the outlet side, are used. A metallic plate 65 is placed in a working position, as shown in FIG. 25. The upper roller 61 moves downward to be pressed to the lower roller 62, thereby pressing so as to hold the metallic plate 65, as shown in FIG. 26. The upper and lower rollers 61 and 62 as a unit pivot in a direction moving the metallic plate 65 away from the inlet assist roller 63, thereby bending the metallic plate 65 at an end thereof, as shown in FIG. 27. The outlet assist roller 64 moves so as to come into contact with the transferred metallic plate 65 at the end thereof, and the upper and lower rollers 61 and 62 are restored to the original position while the upper and lower rollers 61 and 62 rotate so as to transfer the metallic plate 65 toward the outlet side, as shown in FIG. 28. Then, the upper and lower rollers 61 and 62 and the outlet assist roller 64 bend the metallic plate 65, as shown in FIG. 29. The metallic plate 65 is welded at ends thereof (not shown), whereby cylindrical works such as the first and second members 57 and 58 are formed.
However, when the individually manufactured first and second members 57 and 58 are welded so as to form an integral structure, considerable labor and time are required in processes of setting the first and second members 57 and 58 for welding, and sufficient strength cannot be obtained. In addition, the appearance is not good due to the welds of the first and second members 57 and 58 being exposed. Moreover, two sets of bending devices are required because the first and second members 57 and 58 are individually manufactured. Therefore, forging may be used for forming the bearing-receiving unit 53 in an integral structure. However, a forging device is expensive, thereby increasing the cost.
Accordingly, it is an object of the present invention to provide a low-cost bent work and bending method and a bending device therefor, in which a bent work such as a bearing-receiving unit can be manufactured in an integral structure, thereby omitting welding processes and improving the strength and the appearance of the work, and the bent work can be manufactured by one bending device at low cost.
To these ends, according to a first aspect of the present invention, a bent work is obtained by a method comprising the steps of preparing a belt-shaped thick steel material having an L-shaped cross-section; forming a cylinder by bending the belt-shaped thick steel material having an L-shaped cross-section; and welding ends of the belt-shaped thick steel material formed into the cylinder to each other.
According to a second aspect of the present invention, a bending method comprises the steps of providing a belt-shaped thick steel material having one of an L-shaped cross-section and a U-shaped cross-section; and forming the material into a cylinder by using a center roller to be driven to rotate which is positioned and fixed in a predetermined position and a pair of bending rollers to be driven to rotate which is disposed opposing the center roller at one side of the center roller, movable toward and away from the center roller. The belt-shaped thick steel material having one of an L-shaped cross-section and a U-shaped cross-section is bent by being transferred between the center roller and the pair of bending rollers.
According to a third aspect of the present invention, a bending device, for forming a cylinder by bending a belt-shaped thick steel material, comprises a center roller to be driven to rotate positioned and fixed in a predetermined position; and a pair of bending rollers to be driven to rotate disposed opposing the center roller at one side of the center roller, movable toward and away from the center roller, the belt-shaped thick steel material being bent by being transferred between the center roller and the pair of bending rollers. The center roller is provided with an annular recess formed therein around the center roller. The pair of bending rollers are respectively provided with annular convex portions formed thereon around the bending rollers. The convex portions can be inserted in the annular recess of the center roller at a predetermined position of the annular recess of the center roller. The belt-shaped thick steel material having one of an L-shaped cross-section and a U-shaped cross-section is transferred between the center roller and the pair of bending rollers in a manner such that a concave portion of the belt-shaped thick steel material having one of an L-shaped cross-section and a U-shaped cross-section faces toward the outside at the annular recess of the center roller and the convex portions of the pair of bending rollers are positioned in the concave portion of the belt-shaped thick steel material having one of an L-shaped cross-section and a U-shaped cross-section.
According to the present invention, the bent work is formed by bending a belt-shaped thick steel plate having an L-shaped cross-section and welding the steel plate at the ends thereof, thereby forming a cylinder. The cylinder having an L-shaped section can be manufactured in one bending process. It is not necessary to manufacture first and second members 57 and 58 individually, and to combine the first and second members 57 and 58 by welding, as in a known technology. The welding process of assembling the first and second members 57 and 58 can be omitted, according to the present invention. The strength of the bent work according to the present invention is greater than that of the known work because the bent work according to the present invention is integrally formed. The appearance of the bent work is superior to that of the known work in which the welding points of the first and second members 57 and 58 are exposed. The bent work according to the present invention only requires one bending process using one bending device. Because the bent work according to the present invention is formed by bending, the costs are lower than that work which is formed by forging. The bent work according to the present invention may be most appropriately used as a bearing-receiving unit for construction machinery. The steel material used according to the present invention may be a flat steel plate or may be a rolled plate. The rolled plate has an advantage in that a cutting process and the like for making the bent work according to the present invention into a finished product are simple because the shape of the rolled plate can be made, when rolling, close to that of the finished product. The thick steel material includes a steel plate having a thickness of not less than 20 mm. Therefore, the thick steel material does not include a material such as a steel angle.
By the bending method and by the bending device according to the present invention, a cylinder for forming the bent work, which offers the above-described advantages, can be manufactured. By the bending method and by the bending device according to the present invention, when a U-shaped thick steel plate is used, a cylinder formed by bending the U-shaped thick steel plate may be cut at an intermediate part in a direction perpendicular to the axis thereof into two cylinders, yielding two products each having an L-shaped cross-section.
When the bending device has a configuration in which a pressing roller is rotatably disposed opposing a center roller so as to move toward and away from the center roller and to be inserted in an annular recess formed around the center roller at the periphery of the pressing roller, a highly accurately bent work can be obtained by pressing a thick steel material at a thinner portion thereof by the pressing roller so as to prevent the thick steel material from deformation at the thinner portion thereof.